System, method and apparatus for power transmission cable with optical fiber for downhole tool in subterranean applications

ABSTRACT

A system, method and apparatus for incorporating a fiber optic cable into a power cable for an electrical submersible pump is disclosed. The fiber optic components are protected from damage during handling of the cable with pump cable components, such as lead sheaths and jacketing materials. The optical fibers are protected from damage due to corrosive oil well chemicals and gasses, as well as protected from decompression damage.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates in general to power cables and, inparticular, to an improved system, method and apparatus for anelectrical power transmission cable having an optical fiber cable for anelectrical submersible pump or other downhole tools in subterraneanapplications.

2. Description of the Related Art

Many types of electrical tools are used in subterranean applications.For example, electrical submersible pumps (ESP) are used to pump fluidsfrom beneath the earth to the surface. Applications for ESPs and othertypes of downhole tools include geothermal exploration and development,carbon sequestration operations, and oil and gas wells. Such tools aretypically powered by transmission cables that extend a long distancefrom the surface down into the subterranean borehole where the tool islocated.

Power may be transmitted to an ESP by banding a specially constructed,three phase electric power cable to the production tubing. The cable issmall in diameter, well protected from mechanical abuse and imperviousto deterioration of its physical and electrical properties by the hot,aggressive well environments. Cables are available in a wide range ofconductor sizes that permit efficient matching to motor requirements.Such cables can be manufactured in either round or flat configurations,using galvanized steel, stainless steel, or monel armor capable ofwithstanding the hostile environments of an oil well or water well.Solid or stranded electrical conductor construction may be used.

As described herein, the power cables contain several electricalconductors and, in some applications, also contain a smaller fiber opticcable for communications purposes. However, subterranean environmentspresent extreme operational conditions, including certain types ofhighly corrosive chemicals and gasses that readily destroy the physicalintegrity and effectiveness of the fiber optic elements. An improvedsystem, method and apparatus for power transmission cables havingoptical fiber cables for downhole tools in subterranean applicationswould be desirable.

SUMMARY OF THE INVENTION

Embodiments of a system, method, and apparatus for a power cable havingelectrical conductors for downhole tools and fiber optics forcommunications in subterranean applications are disclosed. In someembodiments, the invention provides means for installing fiber opticfilaments in an electrical submersible pump (ESP) assembly that preventsthem from being damaged during ESP cable handling and service.

In one embodiment, a buffered fiber optic filament, i.e., a fiber opticfilament encased in a tube of protective material such as PEA, MEA, PEEKor FEP, is placed inside the insulation of one or more of the electricalconductors of the power cable. This design has the advantage ofprotecting the optical fiber and assuring that it is automaticallydisposed in a helical configuration when the conductor is placed in around cable.

In another embodiment, the buffered fiber optic filament is placedbeneath a lead sheath and on top of the insulation of a single insulatedconductor in one or more of the electrical conductors of the powercable. In some embodiments, the buffered fiber is deployed under thelead sheath in a helix by wrapping it around the insulated conductorprior to applying the lead sheath. The buffered optical fiber also maybe configured in a reversing helix, first going in one direction aroundthe insulated conductor, and then in the opposite direction. This designinsures that the buffered optical fiber is never placed in excessivetension when the conductor is bent, and facilitates applying thebuffered optical fiber in a continuous manner directly behind the leadextruder during manufacturing. In yet another embodiment, the bufferedoptical fiber may be placed in a similar manner directly over the metalconductor and under the insulation prior to applying the insulatinglayer.

The foregoing and other objects and advantages of the present inventionwill be apparent to those skilled in the art, in view of the followingdetailed description of the present invention, taken in conjunction withthe appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features and advantages of the presentinvention are attained and can be understood in more detail, a moreparticular description of the invention briefly summarized above may behad by reference to the embodiments thereof that are illustrated in theappended drawings. However, the drawings illustrate only someembodiments of the invention and therefore are not to be consideredlimiting of its scope as the invention may admit to other equallyeffective embodiments.

FIGS. 1-4 are sectional end views of various embodiments of cablesconstructed in accordance with the invention; and

FIG. 5 is schematic diagram of one embodiment of a subterraneanapplication for cables constructed in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-5, embodiments of a system, method and apparatusfor a power cable having fiber optics for an electrical submersible pump(ESP) or other downhole tools in subterranean applications aredisclosed. The invention comprises a power cable that is designed tooperate in a pressurized subterranean environment that may contain H₂S,methane and/or other corrosive gasses. A buffered fiber optic filamentis isolated from exposure to these gasses by placing the buffered fiberoptic under a hermetically sealed lead sheath. The sheath simultaneouslyprovides protection to the buffered fiber optic filament and theinsulation surrounding the electrical conductors from exposure to theenvironment.

In the embodiment of FIG. 1, a power cable 1 comprises an outer armorlayer 2 having a longitudinal axis and an axial length extending alongthe longitudinal axis. The armor layer 2 may comprise armor that isformed from metallic or other protective materials. A jacket fillingmaterial 3 also is located within an interior of the armor layer 2. Thepower cable 1 further contains a plurality of electrical conductors 4that extend through the outer armor layer 2 along and throughout theaxial length and are cabled about each other in a helical configuration.Each of the electrical conductors 4 is covered with an electricalinsulation 5, such that the electrical conductors 4 are electricallyinsulated from each other. The conductor insulation 5 may be coveredwith other protective tapes and braids or extruded layers 6.

In the illustrated embodiment of FIG. 1, the power cable 1 additionallycontains a buffered optical fiber 7 located inside the electricalinsulation 5 of at least one of the electrical conductors 4.

In FIG. 2, still another embodiment of the invention further comprises alead sheath 8 that is located over the cable insulation 5 and extendsthroughout the lengths of the conductor 4. The buffered optical fiber 7is located radially under the lead sheath 8. The lead sheath 8 islocated around only one of the electrical conductors 4, such that thebuffered optical fiber cable 7 is positioned between the lead sheath 8and the electrical insulation 5 of one or more of the electricalconductors 4.

In additional embodiments, the optical fiber 7 may be helical inconfiguration and wrapped around the electrical insulation 5 of the oneor more electrical conductors 4. Alternatively, the buffered opticalfiber 7 may be configured in a reversing helix, first going in onedirection around the electrical insulation 5, and then in the oppositedirection. In still another alternate embodiment (see, e.g., FIG. 3),the buffered optical fiber cable 7 may be located directly adjacent andin contact with one or more of the electrical conductors 4, and underthe electrical insulation 5 of the electrical conductors 4. Multipleones of these single conductor assemblies can be configured as a flatcable (see, e.g., FIG. 4) or round multi-conductor cable as shown inFIG. 1.

The protection provided by the invention is required for at least tworeasons. First, it is known that hydrogen invades the glass used in theoptical fibers, which lowers their light transmission properties andthereby degrades the fiber optic capabilities. H₂S and other gassesunder the high pressures and high temperatures of a subterraneanenvironment rapidly degrade the optical fibers in this manner. Bysurrounding the fiber optics with an impermeable lead sheath thisdegrading mechanism is eliminated.

Second, the pressures in subterranean environments change rapidly anddramatically, such as when pumps are turned on, or valves are opened.These changes result in rapid reductions in pressure that are generallyreferred to as decompression. Gasses dissolved inside glass fibersexpand during decompression causing fractures in the glass whichseverely degrades its properties. For example, strong fiber glass tapesare placed around power cables and located underground during operation.Upon retrieval to the surface, the glass is often completely broken invery fine pieces due to the decompression mechanism. Again, by placingthe fibers under the lead sheath, this decompression damage isprevented.

FIG. 5 depicts one embodiment of a subterranean application for theinvention. For example, in the illustrated embodiment, a wellinstallation 130 has a number of components located at a surface 138thereof. A power source 119 provides electrical power to a transformer120 and then to a control system 133. A power cable 132, such as thenumerous embodiments described herein, transmits the power downhole to atool, such as subterranean equipment. The tool may comprise, forexample, a pump 122, seal section 124 and motor 126. The pump 122 pumpsfluids to other equipment at the surface 138 as is known by those ofordinary skill in the art.

While the invention has been shown or described in only some of itsforms, it should be apparent to those skilled in the art that it is notso limited, but is susceptible to various changes without departing fromthe scope of the invention. For example, different combinations of thevarious elements of the embodiments described herein may be joinedtogether to form additional alternate embodiments of the invention.

1. A power cable, comprising: an outer armor layer having a longitudinalaxis and an axial length extending along the longitudinal axis; aplurality of electrical conductors extending through the outer armorlayer along the axial length, each of the electrical conductors beingenclosed within a separate electrical insulation layer such that theelectrical conductors are electrically insulated from each other, eachelectrical insulation layer having an inner diameter surface and anouter diameter surface; and a buffered optical fiber extending throughthe cable and located in contact with one of the inner and outerdiameter surfaces of the insulation layer of at least one of theelectrical conductors.
 2. A power cable according to claim 1, whereinthe outer armor layer is a wrapping formed from metallic or otherprotective materials, the buffered optical fiber cable is helicallywrapped around said at least one of the electrical conductors, andfurther comprising a jacket of filling material located in an interiorof the outer armor layer and surrounding the electrical conductors.
 3. Apower cable according to claim 1, further comprising a lead sheathlocated over the insulation layer of said at least one of electricalconductors, and the buffered optical fiber cable is located radiallyinward of the lead sheath and outward of the insulation layer of said atleast one of the insulated electrical conductors.
 4. A power cableaccording to claim 3, wherein the lead sheath is located around only oneof the electrical conductors, and the buffered optical fiber is locatedbetween the lead sheath and the insulation layer of said only one of theelectrical conductors.
 5. A power cable according to claim 3, whereinthe buffered optical fiber is configured in a reversing helix, firstgoing in one direction concentrically around said at least one of theelectrical conductors and then in the opposite direction concentricallyaround said at least one of the electrical conductors.
 6. The powercable according to claim 1, further comprising: a separate protectivelayer concentrically surrounding the electrical insulation layer of saidone of the electrical conductors; and wherein the buffered optical fiberis located between the protective layer and the electrical insulationlayer of said one of the conductors adjacent the outer diameter surfaceof the electrical insulation layer of said one of the conductors.
 7. Thepower cable according to claim 1, wherein the buffered optical fiber islocated between said one of the electrical conductors and the innerdiameter surface of the electrical insulation layer of said one of theelectrical conductors.
 8. A power cable, comprising: an outer armorlayer having a longitudinal axis and an axial length extending along thelongitudinal axis; a plurality of electrical conductors extendingthrough the outer armor layer along the axial length, each of theelectrical conductors being insulated with insulation such that theelectrical conductors are electrically insulated from each other; anoptical fiber cable extending along the axial length of at least one ofthe insulated electrical conductors and located radially exterior to theinsulation; and a lead sheath covering said at least one of theinsulated electrical conductors such that the optical fiber cable islocated radially inward of the lead sheath.
 9. A power cable accordingto claim 8, wherein the outer armor layer is a wrapping formed frommetallic or other protective materials, and further comprising jacketfilling material located in an interior of the outer armor layer.
 10. Apower cable according to claim 8, wherein the power cable is a flatcable.
 11. A power cable according to claim 8 wherein the power cable isround and the electrical conductors are formed in a helix duringassembly to make the power cable more flexible.
 12. A power cableaccording to claim 8, wherein the lead sheath is located around only oneof the electrical conductors, and the optical fiber cable is locatedbetween the lead sheath and the electrical insulation of at least one ofthe electrical conductors.
 13. A power cable according to claim 8,wherein the optical fiber cable is helical in configuration and wrappedaround the electrical insulation of only one of the electricalconductors.
 14. A power cable according to claim 8, wherein the opticalfiber cable is configured in a reversing helix, first going in onedirection and then in the opposite direction.
 15. A power cableaccording to claim 8, wherein the optical fiber cable is locateddirectly adjacent one of the electrical conductors and under theinsulation of said one of the electrical conductors.
 16. A system for asubterranean operation, comprising: an electrical submersible pump forinstallation within a well; a power cable for transmitting electricalpower from a power source downhole to the electrical submersible pump;the power cable comprising: an outer armor layer having a longitudinalaxis and an axial length extending along the longitudinal axis; aplurality of electrical conductors extending through the outer armorlayer along the axial length, each of the electrical conductors beingconcentrically enclosed within a separate electrical insulation layersuch that the electrical conductors are electrically insulated from eachother each of the electrical insulation layers having an inner diametersurface and an outer diameter surface; and an optical fiber cableextending through the outer armor layer in contact with one of the innerand outer diameter surfaces and wrapped helically around and concentricwith one of the electrical conductors.
 17. A system according to claim16, wherein the outer armor layer is a wrapping formed from metallic orother protective materials, and further comprising jacket of fillingmaterial located in an interior of the outer armor layer and enclosingthe electrical conductors.
 18. A system according to claim 16, furthercomprising: a separate protective layer concentrically surrounding theinsulation layer of said one of the electrical conductors; and whereinthe optical fiber cable is positioned between the insulation layer ofsaid one of the electrical conductors and the protective layer.
 19. Asystem according to claim 16, wherein the optical fiber cable isconfigured in a reversing helix, first going in one direction aroundsaid one of the electrical conductors, and then in the oppositedirection around said one of the electrical conductors.
 20. A systemaccording to claim 16, wherein the optical fiber cable is wrappedhelically around the electrical insulation layer of said one of theelectrical conductors.
 21. The power cable according to claim 16,further comprising: a separate protective layer concentricallysurrounding the electrical insulation layer of said one of theelectrical conductors; and wherein the optical fiber cable is locatedbetween the protective layer and the electrical insulation layer of saidone of the conductors.
 22. The power cable according to claim 16,wherein the optical fiber cable is located between said one of theelectrical conductors and the electrical insulation layer of said one ofthe electrical conductors.